Recently, there have been requirements to make a more sensitive magnetic recording medium. If the magnetic recording medium is made more highly sensitive, a high image quality as well as a good sound quality and high density recording can be realized. These improvements can be attained by improving the recording system of a deck used for magnetic recording and reproducing system of a magnetic recording medium and also by improving the magnetic recording medium.
A magnetic recording medium can be highly sensitized by increasing the signal and decreasing the noise in the signal/noise ratio. The signal can be increased by increasing the residual magnetic flux density and coercive force of the magnetic recording media, which can be realized by making the ferromagnetic particles finer or adjusting the shape of anisotropy and the arrangement of the single magnetic domain of each ferromagnetic fine particles.
The noise can be decreased by various factors, for example, by smoothing a magnetic layer and controlling the electrification properties of magnetic recording media. Japanese Patent Publication (Examined) No. 3927/75, Japanese Patent Application (OPI) Nos. 111828/82 and 96505/77 (the term "OPI" as used herein refers to "published unexamined Japanese patent application") and U.S. Pat. No. 4,135,031 disclose that a backing layer can be provided in order to control the electrification properties of a magnetic recording medium and to maintain running durability thereof.
However, it is impossible to obtain a statisfactory magnetic recording medium having high sensitivity and sufficient running durability by the above described technology. There are a number of reasons why it has not been possible to obtain such satisfactory magnetic recording medium: thus (1) although spacing loss between a magnetic recording and reproducing head, and a magnetic recording medium can be reduced by smoothing a surface of the magnetic recording medium, running durability deteriorates and friction coefficient increase, whereby the magnetic layer is peeled part; (2) if a surface of a backing layer is made coarse to improve running durability thereof, the surface roughness of the backing layer is transferred to the magnetic layer. Thereby, the signal/noise ratio of the magnetic layer is decreased; (3) at an initial stage of running of a magnetic recording medium that the magnetic layer and the backing layer are not yet peeled apart, drop out (the term "drop out" herein means such level changes that recording skips instantaneously by dust and powders (hereinafter, referred to as a "scraped powders") which come off from a magnetic layer upon running) increases, thereby decreasing the signal/noise ratio; (4) when a calender forming method is conducted to obtain a smooth surface of a magnetic layer and to obtain a highly sensitive magnetic recording, as disclosed, for example, in U.S. Pat. No. 3,916,039, the backing layer readily is peeled apart, and therefore, it is difficult to manufacture a magnetic recording medium having such a smooth surface on the magnetic layer; and (5) the tape edge becomes waving like a seaweed, after repeated run, thereby deteriorating audio level change.